Interesterification reactions between triglycerides and free fatty acids have been used for upgrading triglyceride fats and oils, e.g., by increasing or decreasing the unsaturation of the fatty acid moieties in the triglyceride molecule. In U.S. Pat. No. 4,275,081, it is disclosed that the reaction may be catalyzed by positionally selective water-soluble microbial lipase enzymes. Prior art catalysts based on alkali metals or alkaline earth metals are also mentioned. It is disclosed that fatty acids liberated from the triglycerides participating in the reaction may be added to the free fatty acids contributing to the rearrangement of the fatty acid moieties on the triglycerides in the feed, but there is no disclosure of separating unreacted unsaturated fatty acids from the reaction effluent to return only the unsaturated free fatty acids to the reaction.
U.S. Pat. No. 3,328,439 discloses the use of chemical catalysts, e.g., natural and synthetic zeolitic aluminosilicates for the interesterification of glyceride oils.
The separation of many classes of compounds by selective adsorption on molecular sieves or zeolites as well as other adsorbents is well known. Also, various separations based on the degree of unsaturation are known, e.g., esters of saturated fatty acids from unsaturated fatty acids with X or Y zeolites exchanged with a selected cation from U.S. Pat. No. 4,048,205 to de Rosset and monoethanoid fatty acids from diethanoid fatty acids with cross-linked polystyrenes, e.g., "Amberlite" from U.S. Pat. No. 4,353,838 to Cleary et al. A process for separating a mixture of triglycerides, based on the iodine values, is shown in U.S. Pat. Nos. 4,277,412 and 4,284,580 in which permutite and aluminated silica gel adsorbents, respectively, can be used. The refining of oils by admixing them with magnesium silicate to adsorb coloring matter and free fatty acids from glyceride oils is disclosed in U.S. Pat. No. 2,639,289.
The use of silica gel in analytical chromatographic separations with various solvent systems is known. Particle sizes of silica gels used in analytical separations ranges from 3 to 10 microns. Also, the removal of various impurities from mixtures including triglycerides is known. Silica gel has been disclosed as an adsorbent for a bulk separation of fatty acids from triglycerides.
U.S. Pat. No. 4,524,029 to Cleary et al discloses a process for separating saturated fatty acids by selective adsorption of the saturated fatty acids onto a silicalite molecular sieve and desorbing the saturated fatty acids with a displacement fluid having a polarity index of at least 3.5. Silicalite is disclosed in Grose et al. U.S. Pat. No. 4,061,724.
U.S. Pat. No. 4,770,819 to Zinnen discloses the separation of diglycerides from triglycerides using an omega zeolite or silica as adsorbent and a ketone having up to 7 carbon atoms mixed with an n-aliphatic hydrocarbon mixture as the desorbent.
The invention herein can be practiced in fixed or moving adsorbent bed systems, but the preferred system for this separation is a countercurrent simulated moving bed system, such as described in Broughton U.S. Pat. No. 2,985,589, incorporated herein by reference. Cyclic advancement of the input and output streams can be accomplished by a manifolding system, which are also known, e.g., by rotary disc valves shown in U.S. Pat. Nos. 3,040,777 and 3,422,848. Equipment utilizing these principles are familiar, in sizes ranging from pilot plant scale (deRosset U.S. Pat. No. 3,706,812) to commercial scale in flow rates from a few cc per hour to many thousands of gallons per hour.
The functions and properties of adsorbents and desorbents in the chromatographic separation of liquid components are well known, but for reference thereto, Zinnen et al U.S. Pat. No. 4,642,397 is incorporated herein.